Liver cancer is a major disease with about 750,000 death per year. Multi-phase Liver CT imaging is a major tool for diagnosis, staging and treatment monitoring. Multiple phases of the contrast agent dynamics are imaged and used to identify different lesion types. The liver has two blood supplies: the hepatic artery and the portal vein. As such, a contrast agent which has been injected at a given time will arrive at two different times in the aortic blood supply and in the portal blood supply of the liver. Since some lesion types behave differently in the contrast agent uptake and washout dynamics, it is of interest to image both the aortic and the portal subnetwork. For instance, whereas the liver parenchyma receives blood mainly from the portal venous system, tumors are usually fed by the hepatic artery.
The problem is that a dedicated CT protocol for evaluation of liver lesions contains up to four scans: a native scan, without any contrast agent, a second scan in the “arterial phase”, when the contrast agent bolus just arrived in the arterial system, a third scan in the “portal venous phase” when the contrast agent bolus arrived through the portal vein, and a final scan when the system reached equilibrium.
Such an amount of scans exposes both the patient and the operators to a tremendous radiation dose which ought to be reduced. The invention addresses this issue while providing a way to calculate an exclusive blood map a first subnetwork of interest, for instance a portal blood map of the liver for evaluation of portal-venous blood supply of liver parenchyma, without contribution from another subnetwork contrast, for instance arterial contrast.
The method according to the invention is especially suited for multi-phase liver imaging but it can be used to image and map any set of blood subnetworks of interest.
It is known from U.S. Pat. No. 8,208,699 to perform multiple contrast agent injections, the delay between the injections being selected so that several regions of interest are predicted to be enhanced approximately at the same time.
Photon counting based spectral CT allows for quantitative and selective imaging of material with K-Edges within the X-Ray spectrum. It has been proposed in the past to use this imaging feature to perform Multi Phase Liver studies with multiple contrast agents. As an example if two contrast agents (CA1, CA2) have been administrated such that during one image acquisition CA1 is already in the portal phase while CA2 is still in the arterial phase. The differentiation of the two contrast agent phases can be performed by using the separation feature of K-Edge imaging. This technique can reduce the number of required scans and will therefore decrease the corresponding radiation dose significantly.